As a storage apparatus for virtual environments, one conventional storage system is present that is capable of realizing a memory device having free volume configuration and storage capacity without being restricted by volume configuration and storage capacity of a physical memory device. This storage apparatus for virtual environments has a real internal storage apparatus controlling access to a physical memory device and creates a virtual volume by a processor that manages the real storage apparatus.
As a measure in the case of disasters, etc., remote copying may be performed by transferring data of a given storage apparatus (local site) to a storage apparatus (remote site) at a remote location. The transfer of data from a copy source (volume) to a copy destination (volume) periodically during the remote copying follows a procedure of first transferring the data from the copy source at a start time to the copy destination and sequentially transferring data updates for the copy source to the copy destination.
The mode by which the data is sequentially transferred is dependent on a requirement concerning a time point when data arrives at the remote site. For example, data may be transferred in synchronization with input/output (I/O) such that the data is transferred each time the data of the copy source is updated, or data may be transferred at regular time intervals asynchronous with I/O, or data may be transferred at arbitrary time intervals asynchronous with I/O.
Assuming that data is transferred to the copy destination as a measure in the case of disasters, the data of the copy source must arrive at the copy destination with the integrity intact. Although the I/O synchronization mode is ideal, when the remote site is farther away, the effect of delay becomes greater at the time of data transfer and therefore, it is difficult to transfer data in synchronization with I/O from a business server, etc.
Thus, in actuality, data transfer to a remote site is an asynchronous transfer. In this case, although the real-time integrity cannot be maintained as in the case of a synchronous transfer, a consistency group is utilized in some cases to group volumes having data desired to be transferred with integrity such that the consistency of the writing order between volumes is ensured at constant time intervals.
To utilize the concept of the consistency group for transferring difference data, a rest point must be obtained for the volumes belonging to the same group. To ensure data used as the rest point, data update requests from a business server to the relevant volumes, etc. are inhibited.
Related technologies include, for example, a data copy system for recovering data in another memory device system even if the data is damaged in one memory device system when remote copying is performed in an unguaranteed order mode. The data copy system checks the integrity at the time of completion of the writing of data from a host computer to a main logical volume of a primary memory device system. The data copy system creates a snapshot recording a state of the main logical volume when the integrity is assured and uses the snapshot to perform remote copying between the primary memory device system and a sub-memory device system. For an example, refer to Japanese Laid-Open Patent Publication No. 2005-293469.
Nonetheless, the conventional technology has a problem of causing delay in I/O from a business server, etc., at the time of remote copying of volumes belonging to a consistency group because a process for maintaining the consistency of the writing order between volumes becomes a bottleneck. For example, if update data for the volumes is stored in one storage area so as to keep the consistency of the writing order between volumes belonging to the consistency group, concentration of access to the storage area forms a bottleneck.